1. Field of the Invention
The invention relates to a battery charging apparatus, and particularly to a battery charging apparatus for controlling charge and discharge of a secondary battery pack and protecting the secondary battery pack from abnormal voltage operation, abnormal current operation and abnormal temperature operation.
2. The Related Art
In recent electronic apparatus, a battery pack containing a secondary battery or a rechargeable battery, such as a lithium-ion battery is often used as the power supply for supplying power to the electronic apparatus. When the time the lithium-ion battery continuous to be charged is too long, the deposition of lithium metal will occur, which damages the battery pack or the electronic apparatus. On the other hand, when the time the lithium-ion battery continues to be discharged is too long, the repetitive charge/discharge operational life of the battery pack will deteriorate.
Please refer to FIG. 6. A conventional battery charging apparatus 800 for controlling charge and discharge of the battery pack 80 has a monitor circuit 81 and a protection switch 82. The battery pack 80 contains plurality of secondary batteries or rechargeable batteries connected in serial. The battery pack 80 and charge/discharge terminals Vio+, Vio− form a charge/discharge path. The protection switch 82 is provided on the charge/discharge path. The monitor circuit 81 connects the battery pack 80 for monitoring charge/discharge condition of the battery pack 80, such as voltage and current of the battery pack 80.
The monitor circuit 81 connects the protect switch 82 for controlling the protect switch 82 to turn off and turn on. Generally, the battery pack 80 supplies power to the electronic apparatus connected between the charge/discharge terminals Voi+, Voi− and the protection switch 82 turns on to bypass power to an electronic apparatus. Also, an external power source connected between the charge/discharge terminals Voi+, Voi− supplies power to the battery pack 80 through the charge/discharge path and the protection switch 82 turns on to bypass power to the battery pack 80. When the monitor circuit 81 detects over-charge condition or over-discharge condition of the battery pack 80, the monitor circuit 81 sets the protection switch 82 turn off to cuts off the charge/discharge patch.
However, the battery charging apparatus 800 can not monitor charge/discharge state of each secondary battery of the battery pack 80. When the time of one secondary battery of the battery pack 80 continuous to be charged and discharged is too long, the battery pack 80 and the electronic apparatus are damaged.